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Home , Lateral lemniscus, Olivocochlear system

Audiologic findings in unilateral deafness resulting from contralateral pontine infarct

KAREN JO DOYLE, MD, PhD, CYNTHIAFOWLER, PhD, and ARNOLD STARR, MD, Irvine and Long Beach, California

Focal brain stem infarction has been uncommonly from April 1994 demonstratd a dorsally located infarct associated with unilateral sensorineural loss involving the medial left portion of the upper , as well (SNHL). Kumar et al. (1986) 1 found a single case of as ischemic changes of the periventricular deep white brain stem infarction among 200 cases of unilateral matter (Figs. 1 and 2). SNHL. Previous case reports of unilateral SNHL He was referred 3 weeks after the stroke to the Audi- ology Department for evaluation of his right-sided hearing after brain stem infarct have been the result of loss. Audiogram revealed a fiat, severe SNHL in the right lesions of the ipsilateral cochlear nuclei in the dor- ear and a moderate high-frequency SNHL above 2000 Hz solateral medulla. 2,3 Wada and Starr (1983) 4 deter- in the left ear (Fig. 3). Speech discrimination was 0% in mined that an experimentally produced lesion of the the right ear and 92% in the left ear. Acoustic reflexes lateral produced a unilateral contralateral were absent in the right ear. ABR was performed with abnormality in the N 3 portion of wave III of the condensation and rarefaction dicks presented 10/second auditory brain stem response (ABR) in guinea pigs. at 95 dB nSL (Fig. 4). In the left ear, all components were We report a case of unilateral SNHL after a con- identified, and their intercomponent times were within tralateral focal pontine infarct verified by magnetic normal limits. In the right ear, wave I was present for resonance imaging (MRI) and ABR testing. condensation clicks at 1.98 msec, and no other waves were identified. Transient and distortion-product otoacoustic CASE REPORT emissions (OAEs) were performed. In the right ear, tran- sient emissions were present with energy present through A 63-year-old man with a history of hypertension was 3000 Hz with 81% reproducibility, similar to those ob- admitted to the Veterans Administration Medical Cen- tained from the left ear (Fig. 5). Distortion-product OAEs ter-Long Beach in June 1994 with a urinary tract infec- (2F2 - F1 = 1.221; F1 = 70 dB SPL; F2 = 70 dB SPL) tion. During his admitting physical examination, a neuro- were present across frequencies in the right ear and logic examination was performed that revealed a right- through F2 = 3000 Hz in the left ear. Repeat MRI with sided hearing loss. The neurologic examination was gadolinium of the internal auditory canals was performed, otherwise normal. He reported that he had had a stroke and they were normal. in April 1994 and had spent several days in another hospital. The records and MRI scans from that hospital- DISCUSSION ization were obtained. The admission physical examina- tion from April revealed a blood pressure of 170/86, a Although we used the combined term sensorineu- central right facial palsy, a right-sided hearing loss, nys- ral hearing loss, the majority of patients with SNHL tagmus (direction not given), and unsteady gait. Labora- have lesions of the sensory apparatus, whereas "neu- tory examination revealed normal cerebrospinal fluid ral" lesions, including degeneration, chemistries and cell counts and negative VDRL. The MRI eighth lesions, and central auditory pathway lesions from the cochlear nuclei to the temporal From the Divisions of Otolaryngology-Head and Neck Sur- cortex, are found less frequentlyJ Among the causes gery and (Drs. Doyle and Fowler), Veterans of hearing loss, cerebrovascular infarction of the Administration Medical Center; and the Departments of auditory pathways has been described infrequently. Otolaryngology-Head and Neck Surgery (Drs. Doyle and A 1986 report of 200 cases of unilateral SNHL found Fowler) and Neurology (Dr. Starr), University of California Irvine. 42 individuals with confirmed retrocochlear lesions, Received for publication April 28, 1995; revision received June of which there was one lesion adjacent to the co- 27, 1995; accepted July 17, 1995. chlear nucleus and a second patient with a pontine Reprint requests: Karen Jo Doyle, MD, PhD, Department of lesion? The most commonly found central lesions in Otolaryngology-Head and Neck Surgery, University of Cali- that study were tumors, cen- fornia Irvine Medical Center, Bldg. 25, Route 81, 101 The City Dr., Orange, CA 02668. tral nervous system lues, and multiple sclerosis. OTOI.A~YNGOI.HZAO NECK SUnG 1996;114:482-6. Lownie and Parnes (1991) 2 found two cases of ipsi- 23/4/67847 lateral SNHL caused by infarcts of the

482 Otolaryngology - Head and Neck Surgery Volume 114 Number 3 DOYLE et al. 483

Fig. I. Coronal T1-weighted MRI of the brain demonstrating left pontine infarct (arrow).

Fig. 2. Axial T2-weighted MRI of the brain demonstrating left pontine infarct (arrow).

and . In both patients there was for the SNHL in 50 patients, 3 of whom had brain significant improvement of the hearing loss in the stem infarcts involving the auditory pathways (one in weeks after infarction. Bales (1989) 3 reported a the cochlear nucleus; the locations of the other two patient with a hearing loss ipsilateral to a pontine were not given). There have been no previous re- infarct who had a moderate-to-severe hearing loss, ports of lesions of the contralateral upper ports poor speech discrimination, and absent waves IV producing hearing loss in human beings. and V, with normal waves I through Ill. The hearing The brain stem auditory pathways are shown in improved l:o normal in 1 month. Armington et al. Fig. 6. The projects to the dorsal and (1988) 6 performed MRI in 176 patients with SNHL ventral cochlear nuclei in the medulla adjacent to and found an abnormality believed to be responsible the inferior cerebellar peduncle. Second-order neu- Otolaryngology - Head and Neck Surgery 484 DOYLE et al. March .I 996

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Fig. 3. Audiogram of patient demonstrating severe right SNHL and poor speech discrimination. Left ear has normal hearing to 2000 Hz and moderately severe high-frequency SNHL. rons decussate to the contralateral medulla through that the patient in this article, who had bilateral the . Fibers then ascend in the lateral high-frequency cochlear hearing loss, had a right- lemniscus in the pons to the of the sided neural hearing loss from a brain stem infarc- . Wada and Start (1983) 4 produced lesions tion in the area of the contralateral pontine lateral of the trapezoid body, , or inferior lemniscus. The timing of the hearing loss at the colliculus in guinea pigs to determine the effects on onset of the stroke, and audiogram, ABR, OAE, and the ABR. Lesions of the trapezoid body produced MRI findings all support this theory. The presumed attenuation of ipsilateral waves III, IV, and V. Le- mechanism of the right-sided hearing loss is inter- sions of the inferior colliculus had no effect on the ruption of the auditory pathway at the contralateral ABR. When unilateral lesions of the lateral lemnis- lateral lemniscus. Because the and cochlear cus were created in 11 animals, ABR to ipsilateral nerve are normal on the right side, OAEs and ABR stimulation was normal, but a loss of the N 3 portion wave I are normal to ipsilateral stimulation in the of wave III evoked by contralateral stimulation was right ear. It is unclear why waves II and III are found, and no changes were noted in waves II or P3. missing to ipsilateral stimulation because they origi- Their previous work in cats had localized P3 to the nate distal to the site of the lesion. Perhaps retro- pons, with components of N 2, P3, and N 3 generated grade neuronal loss occurred. in the brain stem contralateral to the ear stimulated. The patient in this article had normal low-fre- In contrast, Waves I and P2 originate in the ipsilat- quency transient (click) and distortion-product eral cochlear nerve and cochlear nuclei/We posit evoked OAEs. Evoked OAEs are sounds produced Otolaryngol~)y - Head and Neck Surgery Volume ~44 Number 3 DOYLE et al. 485

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Fig. 5. Normal transient OAEs bilaterally through 3000 Hz. Otolaryngology - Head and Neck Surgery 486 DOYLE et al. March 1996

All patients were lacking the normally found sup- CaudalMidbran pression of click-evoked OAEs by continuous con- tralateral white noise that has been attributed to the efferent . They believed that these patients had primary auditory nerve pathway disease with normal outer function. Our case represents the first report of a patient with leftlateral lemniscus unilateral severe hearing loss caused by brain stem infarction, with bilaterally symmetric distortion- ~ product and transient evoked OAEs. This case dem- onstrates the value of OAEs in confirming the di- Mid-Pons agnosis of neural hearing loss. trlgeminaln e we,,..~_.._..., laterallemniscus trapezoidbody ~ REFERENCES 1. Kumar A, Maudelonde C, Mafee M. Unilateral sensory neural hearing loss: analysis of 200 consecutive cases. Laryn- goscope 1986;96:14-32. ( ~ . /UpperMedulla 2. Lownie SP, Parnes SL. Isolated vestibulocochlear dysfunction of central or peripheral vascular origin. Laryngoscope 1991; cochlearn erve ..~'~"~ {~/'~/ 101:1339-42. ventra[cochlearnueleus~~ (~/ 3. Bales JD. Reversible sensorineural hearing loss in a stroke patient. Ear Hear 1989;10:109-11. dorsalcochlear nudeu~ 4. Wada S-I, Starr A. Generation of auditory brain stem re- sponses (ABRs). III. Effects of lesions of the superior olive, Fig. 6. Diagram of the brain stem auditory pathways with lateral lemniscus and inferior colliculus on the ABR in guinea proposed location of infarct {cross-hatched area). pig. Electroencephalogr Clin Neurophysiol 1983;56:352- 66. 5. Gates GA, Popelka GR. Neural presbycusis: a diagnostic by the outer hair cells in response to acoustic tran- dilemma. Am J Otol 1992;13:313-7. sients presented to the ear. 8 Lonsbury-Martin et al. 6. Armington WG, Harnsberger HR, Smoker WRK, Osborn (/991) 9 and Sininger (1993) 1° emphasize the value of AG. Normal and diseased acoustic pathway: evaluation with evoked OAEs in the differentiation of sensory from MR imaging. Radiology 1988;167:509-15. neural hearing loss. Several authors have used 7. Wada S-I, Starr A. Generation of auditory brain stem re- sponses (ABRs). II. Effects of surgical section of the trap- evoked OAEs to confirm neural hearing loss. Bonfils ezoid body on the ABR in guinea pigs and cat. Electroen- and Uziel (1988) 1~ found click-evoked OAEs in sev- cephalogr Clin Neurophysiol 1983;56:340-51. eral patients with acoustic tumors and hearing loss 8. Kemp DT, Bray P, Alexander L, et al. Acoustic emissions worse than 30 dB (cochlear hearing losses greater cochleography-practical aspects. Scand Audiol 1986;25:71- than 30 to 40 dB eliminate click-evoked OAEs), and 95. 9. Lonsbury-Martin BL, Whitehead ML, Martin GK. Clinical Cane et al. (1994) ~z found transient evoked OAEs in applications of otoacoustic emissions. J Speech Hear Res 47% of 45 patients with cerebellopontine angle tu- 1991;34:964-81. mors. Robinette (1992) 13 reported the case of nor- 10. Sininger YS. Clinical applications of otoacoustic emissions. mal click-evoked OAEs present in a patient with Adv Otolaryngol Head Neck Surg 1993;7:247-69. profound hearing loss and multiple sclerosis who 11. Bonfils P, Uziel Z. Evoked otoacoustic emissions in patients with acoustic neuromas. Am J Otol 1988;9:412-7. had a lesion of the auditory nerve as it entered the 12. Case MA, Lutman ME, O-Donoghue GM. Transiently brain stem. Musiek et al. (1994) 14 recorded click- evoked otoacoustic emissions in patients with cerebellopon- evoked OAEs in a "centrally deaf" patient. Starr et tine angle tumors. Am J Otol 1994;15:207-10. al. (1993) 15 reported the case of a child with mod- 13. Robinette MS. Clinical observations with transient evoked otoacoustic emissions with adults. Semin Hear 1992;13:23- erate hearing loss by pure-tone audiogram who had 36. no ABR to stimuli up to 90 dB nHL but who had a 14. Musiek FE, Smurzynski J, Bornstein SP. Otoacoustic emis- dear cochlear microphonic and robust OAEs. Ber- sions testing in adults: an overview. Am J Otol 1994;15:21-8. lin et al. (1994) 16 presented five cases of adults with 15. Starr A, McPherson D, Patterson J, et al. Absence of both bilateral SNHL, absent ABR in four of the patients auditory evoked potentials and auditory percepts dependent on timing cues. Brain 1991;114:1157-80. (wave I only was present in the fifth patient), and 16. Berlin CI, Hood I J, Hurley A, Wen H. Contralateral sup- normal click-evoked OAEs. Three of these patients pression of otoacoustic emissions: an index of the function of had Charcot-Marie-Tooth disease, and the cause of the medial olivocochlear system. OTO~mV~GOLHEm NECK hearing loss in the other two remained undiagnosed. S~rt6 1994;110:3-21.